(a) Field of the Invention
The present invention relates to a plasma display panel, and in particular, to a protective layer for a plasma display panel with improved performance characteristics.
(b) Description of Related Art
Generally, a plasma display panel (PDP) is a display device which displays characters or graphics. In operation, a predetermined voltage is applied across two electrodes placed within the discharge space of the plasma display panel with the resulting plasma discharge generating ultraviolet light. The ultraviolet light excites a phosphor film to generate visible light of a predetermined pattern, thereby displaying the desired images.
Plasma display panels are generally classified as an AC type, a DC type or a hybrid type. FIG. 10 is an exploded perspective view of a discharge cell of a common AC type plasma display panel. As shown in FIG. 10, the plasma display panel 100 includes a front (or rear) substrate 111, a plurality of address electrodes 115 formed on the bottom substrate 111, a dielectric layer 119 formed on the substrate 111 with the address electrodes 115, a plurality of barrier ribs 123 formed on the dielectric layer 119 to maintain the discharge distance while preventing the inter-cell cross talk, and a phosphor layer 125 formed on the barrier ribs 123.
A plurality of discharge sustain electrodes 117 are formed on a front substrate 113 facing the rear substrate 111 such that they are spaced apart from the address electrodes 115 by a predetermined distance while perpendicular thereto. A dielectric layer 121 and a protective layer 127 sequentially cover the discharge sustain electrodes 117. The protective layer 127 is typically formed from MgO, which is transparent such that visible light can pass through. It is known that such a MgO-based protective layer 127 can protect the dielectric layer 121 while maintaining excellent electron emission capacity. Recently, other materials have been also investigated for use in forming a protective layer 127.
The MgO protective layer is provided at a thickness of 3,000 to 7,000 Å and protects the dielectric layer from ion bombardment, and emits secondary electrons to lower the discharge voltage. The MgO protective layer is formed using various techniques such as sputtering, electron beam deposition, ion beam assisted deposition (IBAD), chemical vapor deposition (CVD), and sol-gel, and recently, the ion plating technique.
With the electron beam deposition technique, the electron beams accelerated by the electromagnetic fields collide against the MgO depositing material to heat and vaporize it, thereby forming a MgO protective layer. Compared to the electron beam deposition technique, the sputtering technique makes the resulting protective layer denser and provides improved crystal alignment, but involves high production costs. With the sol-gel technique, the MgO protective layer is formed with a liquid phase.
As an alternative to the various techniques of forming the MgO protective layer, the ion plating technique has been recently introduced with the steps of ionizing evaporated particles and forming a layer. The ion plating technique is similar to the sputtering technique in that it gives the properties of adherence and crystallinity to the resulting MgO protective layer, but differs from the latter in that it provides an advantage in making the deposition at high speed on the order of 8 nm/s.
The MgO material may be formed with a single crystalline phase or a sintered one. When the single crystalline MgO material is melted to make the deposition, it is difficult to control the concentration of dopants because the solid solution is limited by the cooling speeds. Therefore, the MgO protective layer is often formed by using the sintered MgO material where the relevant dopants are quantitatively added, based on the ion plating technique.
As the MgO protective layer contacts the discharge gas, the amount of MgO and its layer formation conditions may greatly influence the discharge characteristics and the performance characteristics of the MgO protective layer. Accordingly, it is desired to find an optimum material composition for the protective layer, which is well adapted for obtaining the desired performance characteristics.